In frequency bands with low communication quality (communication line quality), such as the short-wave band, it is very important to communicate at the optimum frequency. For example, in the disclosure of Unexamined Japanese Patent Application KOKAI Publication No. H4-313926 discloses a technology which chooses (selects) a frequency with high communication quality by successively observing the radio wave condition of usable frequencies and, when observation results indicating the radio wave condition of that frequency falls below a prescribed level, automatically selects another frequency.
However, short-wave band communications primarily use ionosphere reflection, but the condition of the ionosphere changes moment by moment depending on the time, region, season, number of sunspots and so forth, so the optimum frequency for communications is constantly changing. With the composition disclosed in Patent Literature 1, another frequency is automatically selected when observation results showing radio wave conditions drop below a prescribed level, so when the frequency during a call is not the optimum frequency, there are times when the call becomes difficult due to frequent switching of the frequency. For this reason, a new method is needed for selecting the optimum frequency even when the radio wave condition has changed.
In consideration of the foregoing, it is an object of the present invention to provide a suitable wireless communication apparatus and wireless communication method for selecting the optimum frequency even when the radio wave condition has changed.